This invention is generally directed to photoresponsive imaging members, and more specifically the present invention is directed to improved photoresponsive imaging members containing as hole transporting substances polygermane homopolymers, or copolymers of polygermanes and polysilylenes, as well as mixtures thereof. In one important embodiment of the present invention there is provided a layered photoresponsive imaging member comprised of a polygermane homopolymer or copolymer, a charge transporting layer and a photogenerating layer, which members are particularly useful in electrophotographic, including xerographic, imaging and printing processes. Further, there is provided in one particular aspect of the present invention an improved layered photoresponsive imaging member comprised of a supporting substrate, a photogenerating layer, and in contact therewith a hole transporting layer comprised of polygermane components. In addition, as charge transporting compounds there can be selected for the imaging members of the present invention the copolymers of polygermanes dispersed in organosilylenes. With further respect to the aforementioned imaging members, the polygermane or copolymer hole transporting compound layer can be located as the top layer of the imaging member of alternatively may be situated between the supporting substrate and the photogenerating layer. Moreover, the imaging members of the present invention are useful in electrophotographic, and especially xerographic imaging and printing processes, including particularly those wherein liquid developer compositions and dry developer compositions as selected for rendering the formulated image visible.
The formation and development of electrostatic latent images on the imaging surfaces of photoconductive materials by electrostatic means is well known. The photoreceptor selected may comprise a conductive substrate containing on its surface a layer or layers of photoconductive insulating materials, and in many instances there can be used a thin barrier layer situated between the substrate and the photoconductive layer to prevent charge injection from the substrate into the photoconductive layer upon charging. Numerous different photoconductive members for use in xerography are known, including for example a homogeneous layer of a single material such as vitreous selenium, or composite layered imaging members with a photoconductive compound dispersed in other substances. An example of one type of composite photoconductive layer used in xerography is described, for example, in U.S. Pat. No. 3,121,006 wherein there is disclosed a number of layers comprising finely divided particles of photoconductive inorganic compounds dispersed in an electrically insulating organic resin binder.
There are also known photoreceptor materials comprised of other inorganic or organic materials wherein the charge carrier generation and charge carrier transport functions are accomplished by discrete contiguous layers. Additionally, photoreceptor materials are disclosed in the prior art which includes an overcoating layer of an electrically insulating polymeric material, and in conjunction with this overcoated type photoreceptor there have been proposed a number of imaging methods. However, the art of xerography continues to advance, and more stringent demands need to be met by the copying apparatus to permit an increase in performance standards especially with liquid developer compositions, and to permit higher quality images. The photoconductive imaging member of the present invention represents such an improved member, and has other advantages as disclosed hereinafter.
Recently, there have been developed layered photoresponsive imaging members, including those comprised of generating layers and transport layers as disclosed in U.S. Pat. No. 4,265,990, and overcoated photoresponsive materials with a hole injecting layer overcoated with a transport layer, followed by an overcoating of a photogenerating layer and a top coating of an insulating organic resin, reference U.S. Pat. No. 4,251,612. Examples of photogenerating layers disclosed in these patents include trigonal selenium and metal, or metal free phthalocyanines. Illustrative examples of the transport compounds that may be employed are comprised of certain aromatic amines as mentioned therein. The disclosures of each of these patents, namely U.S. Pat. Nos. 4,265,990 and 4,251,612, are totally incorporated herein by reference. The 990 patent is of particular interest in that it discloses layered photoresponsive imaging members similar to those illustrated in the present application with the exception that the hole transporting substances of this patent are comprised of aryl amine compositions, while in accordance with the present invention the hole transporting substance is comprised of, for example, a polygermane.
Many other patents are in existence describing photoresponsive imaging members including layered imaging members with generating substances such as U.S. Pat. No. 3,041,167, which describes an electrophotographic imaging member with an overcoated imaging member containing a conductive substrate, a photoconductive insulating layer, and an overcoating layer of an electrically insulating polymeric material. This member is utilized in an electrophotographic copying method by, for example, initially charging the member with an electrostatic charge of a first polarity, and imagewise exposing to form an electrostatic latent image which can be subsequently developed to form a visible image.
In U.S. Pat. No. 3,041,116 there is disclosed a photoconductive material with a transparent plastic material overcoated on a layer of vitreous selenium, which is present on a recording substrate. Apparently, in operation the free surface of the transparent plastic is electrostatically charged to a desired polarity, followed by exposing the imaging member to activating radiation, which generates a hole electron pair in the photoconductive layer, and wherein the electrons move to the plastic layer and neutralize the positive charges contained on the free surface of the plastic layer, thus creating an electrostatic image. Also, there is disclosed in U.S. Pat. Nos. 4,232,102 and 4,233,383, the disclosures of which are totally incorporated herein by reference, the use of sodium carbonate doped and barium carbonate doped photoresponsive imaging members containing trigonal selenium. Other representative patents disclosing layered photoresponsive imaging members include U.S. Pat. Nos. 4,115,116; 4,047,949 and 4,081,274.
In addition, there are also known layered photoresponsive imaging members wherein there are selected various squaraine compounds, reference for example U.S. Pat. Nos. 4,552,822; 4,415,639; 4,471,041; and 4,486,520, the disclosures of each of these patents being totally incorporated herein by reference.
There are also illustrated in U.S. Pat. No. 4,618,551, the disclosure of which is totally incorporated herein by reference, photoresponsive imaging members comprised, for example, of supporting substrates and charge transport layers containing therein polysilylenes. More specifically, there is illustrated in the aforementioned patent a polysilylene hole transporting compound for use in imaging members, which compound is of the formula as illustrated in claim 1 with specific examples of polysilylenes being poly(methylphenyl silylene) of an average molecular weight of greater than 50,000.
Although imaging members with various hole transporting substances, including aryl amines and polysilylenes, are suitable for their intended purposes, there continues to be a need for improved members, particularly layered members which are comprised of specific polygermanes, and copolymers thereof, and which are compatible with a variety of photogenerating pigments. There is also a need for improved imaging members with specific polygermanes that possess low ionization potentials thereby enabling the effective and efficient transporting of the holes in the imaging members.
Moreover, there continues to be a need for specific layered imaging members which not only generate acceptable images, but which can be repeatedly used in a number of imaging cycles without deterioration thereof from the machine environment or surrounding conditions. Additionally, there continues to be a need for improved layered imaging members wherein the materials employed for the respective layers, particularly the hole transporting layer, are substantially inert to the users of these members. Further, there continues to a need for improved photoresponsive imaging members which can be prepared with a minimum number of processing steps, and wherein the layers are sufficiently adhered to one another to allow the continuous use of these imaging members in repetitive imaging processes. Also, there continues to be a need for new hole transporting compounds that are also useful as protective overcoating layers, and as interface materials for various imaging members. There also is a need for new hole transporting substances which enable increased mobility of holes in layered imaging members. Likewise, there is a need for hole transporting compounds with increased stability, for example, wherein there is no extraction of these compounds from the layered imaging members in which they are incorporated when, for instance, liquid developers are selected for rendering the latent electrostatic latent image visible. Furthermore, there is a need for hole transporting compounds useful in layered imaging members, which compounds are superior insulators in the dark compared to may other known hole transporting compounds, thus enabling charging of the resulting imaging member to higher fields while maintaining cyclic stability, and allowing improved developability. Also, there is a need for imaging members with new hole transporting compounds which can function as resinous binders. Additionally, there is a need for enabling the preparation of imaging members with polygermane hole transporting compounds, or copolymers thereof, which preparation allows for the selection of a variety of solvents, inclusive of toluene, benzene, tetrahydrofuran, cyclohexane, and halogenated solvents in addition to methylene chloride.